Re: Hitachi HD6303 target

[Andrew Haley <aph at cambridge dot redhat dot com>]

tm writes:
 > 
 > John Carter wrote:
 > 
 > >I have been given the opportunity to create a cross compiler to ye olde
 > >16 bit Hitachi HD 6303 CPU.
 > 
 > >It's best known incarnation is probably the Psion
 > >Organizer II (although I would be using it in a weird embedded thing).
 > 
 > >Allegedly it is similar in instruction set to the Motorola 6805
 > 
 > >Questions to the list:
 > >- Wild guess as to the number of man days to do such a thing
 > >- Is there any C compiler for this thing?
 > >- Is there any gcc port or partial port for this thing?
 > >- Is there any gcc port or partial port for the 6805?

The 6085 is even harder.  IMO the 6801 would be hard, the 6805 near
impossible.  It has a 6-bit stack pointer and an 11-bit program
counter, I think.

 > >- Given that this is a slow, register starved, tiny memory space (64k 
 > >  address space) beastie, would targetting gcc to it be the right thing? 
 > 
 > You would probably emulate a machine with general-purpose registers
 > and emit multiple native instructions to move stuff in/out of the
 > emulated gp registers.

The 6303 (a 6801 variant IIRC) has a fairly small memory space, and
the instruction set is such that the code to spill a variable to a
stack slot will be long.  Better make sure you have a huge number of
virtual registers to make that never happens.  It's possible that
you'd run out of memory quite quickly with moderately complex program.

Instead, it's a good idea to create an interpreter that can
efficiently be implemented on a 6801 and then do a gcc back end for
that.  Profile a few applications, and then tweak the architecture of
the virtual machine as necessary.

 > >- Would it be easier retarget a forth implementation?
 > 
 > Probably a factor of two to four easier IMHO to do a Forth implementation.

Probably, and on such a beast it's an easier way to get things done.
You have to think about a debugger, don't forget...

Andrew.